Astronomy Picture of the Day

    Discover the cosmos! Each day a different image or photograph of our
      fascinating universe is featured, along with a brief explanation
                    written by a professional astronomer.

                               2020 November 7

                      The Hercules Cluster of Galaxies
                  Image Credit & Copyright: Howard Trottier

   Explanation: These are galaxies of the Hercules Cluster, an archipelago
   of island universes a mere 500 million light-years away. Also known as
   Abell 2151, this cluster is loaded with gas and dust rich, star-forming
   spiral galaxies but has relatively few elliptical galaxies, which lack
   gas and dust and the associated newborn stars. The colors in this deep
   composite image clearly show the star forming galaxies with a blue tint
   and galaxies with older stellar populations with a yellowish cast. The
   sharp picture spans about 1/2 degree across the cluster center,
   corresponding to over 4 million light-years at the cluster's estimated
   distance. Diffraction spikes around brighter foreground stars in our
   own Milky Way galaxy are produced by the imaging telescope's mirror
   support vanes. In the cosmic vista many galaxies seem to be colliding
   or merging while others seem distorted - clear evidence that cluster
   galaxies commonly interact. In fact, the Hercules Cluster itself may be
   seen as the result of ongoing mergers of smaller galaxy clusters and is
   thought to be similar to young galaxy clusters in the much more
   distant, early Universe.

                       Tomorrow's picture: a dark moon
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       Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (UMCP)
            NASA Official: Phillip Newman Specific rights apply.
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                             & Michigan Tech. U.

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